distinctive points or markings (on the ground), whose positions (coordinates) are known and which are visible on photos or images -- used to help correctly position the photography or imagery for mapping or GIS

Used to help rectify or geolocate photography or imagery, ground control is a set of distinctive points or markings on the ground that are visible on the photos or images and whose positions (coordinates) are known.

In photogrammetric mapping, ground control points are accurately positioned via traditional survey methods or, more likely, modern GNSS methods (e.g., GPS) and the rectification process typically involves sophisticated mathematical models that spatially relate the ground being mapped, the geometry of the camera, and the images or photographs.

In cruder methods, control point positions may even be measured from existing maps and the relationships between maps and images determined by coordinate transformation estimation techniques.

history | excerpt history